1. Field of the Invention
This invention relates to catheter assemblies, and more particularly, to self-inflating or autoinflating balloon catheters within the catheter and balloon assembly, including means for automatically regulating the fluid pressure inside the autoinflating balloon.
2. Description of the Related Art
Catheters have long been used in a wide variety of medical procedures in which the catheter is received in a bodily orifice to conduct fluid by way of the orifice. An example of one such procedure is known as retrograde cardioplegia solution perfusion. The catheter employed is provided with a selectively inflatable cuff or balloon adjacent the distal tip of the catheter. The distal tip is formed with one or more fluid outlets for the discharge of fluid from the catheter assembly. When the distal tip and the balloon are inserted in the coronary sinus and are properly situated, the balloon is inflated to occlude the sinus and to retain the catheter therein. Typically, the catheter and balloon are introduced into the coronary sinus as blood is naturally flowing through it in the opposite direction. Once the balloon has been inflated to occlude the coronary sinus, cardioplegia solution is forced through the catheter to exit through the outlet at the distal tip and perfuse the heart by way of the cardiac veins.
Many different balloon catheter assemblies have been developed for this procedure, but they can be divided between those having manually inflated balloons and those provided with xe2x80x9cself-inflatingxe2x80x9d or xe2x80x9cautoinflatingxe2x80x9d balloons. Manual inflation is accommodated by manufacturing the catheter assembly with a secondary lumen in communication with the interior of the balloon. Autoinflating balloons are automatically inflated by means of a fluid interconnection between the catheter lumen and the interior of the balloon. Most autoinflating balloons are preformed so that the body portion of the balloon extends radially outwardly from the catheter body even in the relaxed condition. However, most manual inflation balloons are formed of an elastomeric material such as silicone so that substantially the entire balloon is tightly received around the body of the catheter in the relaxed position and must be inflated or expanded radially in order to occlude the coronary sinus.
Examples of such catheters are disclosed in U.S. Pat. No. 5,385,548, issued Jan. 31, 1995 to C. R. Williams et al., U.S. Pat. No. 5,197,952, issued Mar. 30, 1993 to S. J. Marcadis et al., and U.S. Pat. No. 4,917,667, issued Apr. 17, 1990 to J. Jackson.
Prior balloon designs may present one or more of several problems. For example, preformed balloons are typically larger in the relaxed state than the opening of the coronary sinus. Therefore, the balloon is difficult to insert into the coronary sinus and may cause trauma to the tissue as it is inserted. Eliminating the preformed balloon may reduce the trauma the tissue endures during insertion of the balloon. In a catheter having a manually inflated balloon, the balloon may be made of a tightly fitting elastomeric material. Heretofore, however, tightly fitting elastomeric balloons have not been employed in autoinflating catheter balloon assemblies because no effective means were known for controlling the inflation rate of the elastomeric balloon.
The catheter assembly according to the invention overcomes the problems of the prior art by creating an autoinflating balloon with means for automatically regulating the internal pressure of the balloon in response to the pressure differential between the interior and exterior of the balloon.
The invention comprises a balloon catheter having a catheter body and a balloon secured to the exterior surface of the body. The catheter body has a lumen formed therein with a fluid discharge aperture formed in the body for discharging fluid from the lumen. The balloon is expandable between a relaxed, contracted state and an expanded state in response to a pressure differential between the interior of the lumen and exterior of the balloon. The catheter body is formed with a balloon inflation aperture fluidly interconnecting the lumen and the interior of the balloon. In order to automatically control the inflation rate of the balloon and fluid flow rate of fluid from the catheter, an autoregulation valve is provided on either the balloon or the catheter body. The valve is adapted to seal the fluid discharge aperture and thereby preclude the discharge of fluid from the lumen at a pressure differential lower than a predetermined fluid pressure differential. The autoregulation valve establishes a fluid flow path between the lumen and the fluid discharge at pressure differentials equal to or greater than the predetermined level.
Preferably, the autoregulation valve is adapted to enlarge the cross-sectional area of the fluid flow path discharge as the fluid pressure differential between the inside and outside of the balloon continues to rise above the predetermined differential.
In one embodiment, the fluid discharge aperture is formed in a fluid flow channel provided in the catheter body adjacent to the balloon. The outer end of the fluid flow channel opens to the exterior of the catheter body. The autoregulation valve comprises an inner end of the fluid flow channel and a portion of the balloon surrounding the inner end of the fluid flow channel so that fluid inside the lumen is prevented from entering the fluid flow channel for discharge from the assembly when the balloon is in the relaxed, uninflated state. The balloon is expandable in response to an increase in fluid pressure in the lumen above the pressure on the exterior of the balloon. Above a predetermined differential, the inner end of the fluid flow channel opens to the interior of the balloon to discharge fluid from the lumen by way of the interior of the balloon and the fluid flow channel.
Preferably, the fluid flow channel comprises a groove formed on the exterior surface of the catheter body wherein the groove is tapered so that the cross-sectional area of the outer end of the groove is greater than the cross-sectional area of the inner end thereof.
Preferably, the distal end of the balloon surrounds the inner end of the groove and is radially expandable and longitudinally extendable so that the portion of the groove which is exposed to the hollow interior of the balloon in the expanded state varies as a function of the radial expansion and longitudinal extension of the balloon. This extension and expansion is in response to increases in fluid pressure inside the balloon.
In an alternative embodiment, the proximal end of the balloon is secured to the exterior surface of the catheter body and the autoregulation valve comprises a member mounted to the distal end of the balloon and slidably mounted on the distal end of the catheter body. The fluid discharge aperture is formed on the sliding member. A second lumen formed on the sliding member is in fluid communication with the catheter lumen and the fluid discharge apertures. The slidable member is adapted to slide axially relative to the catheter body in response to varying pressure differentials between the interior and exterior of the balloon. The fluid discharge aperture is disposed on the slidable member so that the aperture is closed to fluid communication with the catheter lumen when the balloon is in the relaxed state. The fluid discharge aperture is adapted to be open to fluid communication with the catheter lumen when the fluid pressure differential is sufficient to extend the slidable member a sufficient distance to expose the fluid discharge aperture to the catheter lumen.
In an alternative embodiment, multiple fluid discharge apertures are provided longitudinally along the slidable member whereby the effective area of the fluid discharge aperture will vary with the relative extension of the sliding member in response to increasing fluid pressure within the catheter lumen.
In still another embodiment, the autoregulation valve comprises a one-way valve provided in the catheter lumen. The valve includes a valve member selectively seated in a tapered seat provided within the catheter lumen, proximally of the fluid discharge aperture. The tapered seat is formed with a valve aperture therein in fluid communication with the lumen and having an internal diameter smaller than that of the lumen. A valve member is disposed within the catheter lumen distally of the seat. A valve spring is disposed within the catheter lumen distally of the valve member and adapted to bias the valve member into seating engagement with the seat. The spring is selected to close the valve aperture at fluid pressure differential levels below the predetermined fluid pressure differential and to permit the valve member to be lifted from engagement with the valve seat at fluid pressure differential levels equal to or greater than the predetermined differential. With the valve member so displaced, the fluid discharge aperture is open to the flow of fluid from the lumen.
In yet another embodiment, the autoregulation valve comprises a one-way duckbill valve provided in the catheter lumen. The duckbill valve comprises a pair of tapered valve members extending inwardly from the insides of the lumen. The tapered ends of the valve members abut one another to close the fluid flow path through the lumen. The elastic reaction of the valve members is designed so that the valve members will remain closed until the pressure differential between the interior of the lumen and the exterior of the lumen exceeds a predetermined level. Once this level has been exceeded, the tapered members will part from one another, establishing fluid communication between the fluid discharge aperture and the body of the catheter lumen.